This invention is directed to an improvement in a thermal power plant which produces, during periods of low loads by use of its excess energy, compressed air which is accumulated in a storage tank and withdrawn again at the time of peak loads for the generation of additional energy, where the compressed air, after heating, drives a hot-air turbine, acting as power gas.
Recently, compressed-air storage has been proposed as a support for peak loads in connection with thermal power plants. Nuclear power plants, for example, cannot be shut down overnight, and excess energy is therefore available during the period of low loads, to be stored in a suitable manner and subsequently utilized as a support for peak loads. In areas where water is available and sufficient differences in height exist, hydraulic pumped storage systems can, and have been constructed for a long time. In flat areas such systems can be constructed only at great costs, provided this is feasible at all geologically. In such cases a compressed-air storage will be the proper solution. It is known for example -- see Brown Boveri Mitteilungen 62, (1975) pages 332 to 337 -- to compress air during the periods of low loads and to store this air in an underground cave. In order to cover the day-time peak load, the compressed air is fed into the combustion chamber of a gas turbine plant and the energy stored in this manner is converted into electric energy. Plants of this type require high-quality fuels and the costs for such special fuels are considerable. In Europe these costs are at least equal to the amount of all other costs for the operation of the power plant.
There is also known a power plant arrangement where the heat of compression contained in the compressed air is transferred to an underground heat storage facility prior to its flow into the compressed-air storage. Any air that is withdrawn later on from the storage, will flow again through the heat storage where it is heated up and then fed into a hot-air turbine. This specific system has the disadvantage that it will not be possible to provide any inter-cooling in the compressor because the heat is needed for the operation of the turbine. As a result thereof, the drive of the compressor will consume a great amount of energy. Furthermore, the construction of an underground heat storage facility leads to various difficulties and problems.